As hydrocarbon wells are developed, chemicals are often used throughout the process ranging from drilling, fracturing, completions, acidizing and work over. In drilling process alone for example, there are varieties of polymeric gelling and viscosifying agents one should choose from in order to enhance the rheological and gelling properties of the drilling mud.
Formulation of drilling fluids or drilling mud is one of the most important aspects in drilling engineering. This is because the drilling fluids are capable of lubricating and cooling the drill bit and drill string as well as carrying cuttings out of the borehole. All of these functions require appropriate viscosity of drilling fluids to facilitate pumping, circulate the cuttings and transfer them to the surface. Apart from that, adequate gelling property of the drilling fluids is also required to prevent drill cuttings from settling down at the bit. This necessitates suspend drill cuttings in the borehole when the circulation is stopped due to any reason.
Some of the chemicals or additives commonly used as a drilling mud gelling and viscosifying agents are carboxymethyl cellulose (CMC), xanthane and guar gum. However, these commercial drilling additives are subjected to thermal and biological degradation at temperature above approximately 140° C. They are usually mixed with water which should be low in temperature and free of enzyme and bacteria. Furthermore, they are alkaline in pH which requires to be adjusted to desired pH range via pH controlling agent. Thus, these commercial drilling additives will generate environmental problems and increase the toxicity in the drilling field. Drilling workers are probably the most at risk while handling drilling operation. It is even worse when lost circulation problem occurs down-hole, where these toxic materials could enter the formation and contaminate ground water supply.
Due to widespread use of drilling additives in oil and natural drilling activities, environmental and economical concern towards wells development projects are increasingly becoming important in recent years. Efforts are needed to be taken seriously in order to minimize the chance of getting into environmental and economical problems.
There are several patented technologies disclosed in the prior arts relating to drilling mud or its additives. U.S. Pat. No. 4,374,738 relates to a drilling fluid composition which comprises an aqueous dispersion of a clay material containing an effective dispersing amount of a modified lignosulfonate. This modified lignosulfonate is obtained by graft polymerization of from 5 to 30 weight percent of an acrylic compound with the lignosulfonate. However, this invention only aims to provide a chrome-free drilling fluid composition with thermal stability, there is no method provided for preparing a drilling mud additive or composition using a more simple and more environmentally friendly method. The lignosulfonate used in this invention is a calcium-based fermented spent sulfite liquor which is to be processed by a complication procedure.
Another U.S. Pat. No. 5,037,931 also relates to a soluble or crosslinked graft copolymer of lignin acrylamide and hydroxymethacrylate. This graft copolymer is designed to have a particular range of molecular weight suitable for use as thickeners for water and aqueous solutions, recovery of oil from subterranean wells, drilling fluid compositions or in plastics and elastomers. However, this invention only focuses on the preparation of copolymer of lignin using various reagents and percentages, it does not provide any technical guidance on the optimization of the performance of this graft copolymer as a drilling mud additive.
The need of an effective and environmentally friendly gelling and viscosifying agent for drilling mud is increasing due to various economical and environmental concerns. As LGC is deemed a good pH controlling and thermal degradation-resistant gelling and viscosifying agent, it is desirable for the present invention to provide a more innovative, efficient and cost-saving method for preparing the LGC. Besides, an effective formulation of drilling mud containing LGC is also desired. Meanwhile, the problems relating to the environment such as the disposal of oil palm lignocellulosic wastes shall also be overcome by recycling these unwanted materials into valuable products.